The Role of Parasitism in Adaptive Radiations—When Might Parasites Promote and When Might They Constrain Ecological Speciation?

Research on speciation and adaptive radiation has flourished during the past decades, yet factors underlying initiation of reproductive isolation often remain unknown. Parasites represent important selective agents and have received renewed attention in speciation research. We review the literature on parasite-mediated divergent selection in context of ecological speciation and present empirical evidence for three nonexclusive mechanisms by which parasites might facilitate speciation: reduced viability or fecundity of immigrants and hybrids, assortative mating as a pleiotropic by-product of host adaptation, and ecologically-based sexual selection. We emphasise the lack of research on speciation continuums, which is why no study has yet made a convincing case for parasite driven divergent evolution to initiate the emergence of reproductive isolation. We also point interest towards selection imposed by single versus multiple parasite species, conceptually linking this to strength and multifariousness of selection. Moreover, we discuss how parasites, by manipulating behaviour or impairing sensory abilities of hosts, may change the form of selection that underlies speciation. We conclude that future studies should consider host populations at variable stages of the speciation process, and explore recurrent patterns of parasitism and resistance that could pinpoint the role of parasites in imposing the divergent selection that initiates ecological speciation.

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Habitat Choice and Speciation

International Journal of Ecology ◽

10.1155/2012/154686 ◽

2012 ◽

Vol 2012 ◽

pp. 1-12 ◽

Cited By ~ 24

Author(s):

Sophie E. Webster ◽

Juan Galindo ◽

John W. Grahame ◽

Roger K. Butlin

Keyword(s):

Reproductive Isolation ◽

Local Adaptation ◽

Ecological Speciation ◽

Habitat Choice ◽

Current Evidence ◽

Evolutionary Mechanisms ◽

Important Challenge ◽

Intertidal Gastropod ◽

Underlying Mechanisms

The role of habitat choice in reproductive isolation and ecological speciation has often been overlooked, despite acknowledgement of its ability to facilitate local adaptation. It can form part of the speciation process through various evolutionary mechanisms, yet where habitat choice has been included in models of ecological speciation little thought has been given to these underlying mechanisms. Here, we propose and describe three independent criteria underlying ten different evolutionary scenarios in which habitat choice may promote or maintain local adaptation. The scenarios are the result of all possible combinations of the independent criteria, providing a conceptual framework in which to discuss examples which illustrate each scenario. These examples show that the different roles of habitat choice in ecological speciation have rarely been effectively distinguished. Making such distinctions is an important challenge for the future, allowing better experimental design, stronger inferences and more meaningful comparisons among systems. We show some of the practical difficulties involved by reviewing the current evidence for the role of habitat choice in local adaptation and reproductive isolation in the intertidal gastropodLittorina saxatilis, a model system for the study of ecological speciation, assessing whether any of the proposed scenarios can be reliably distinguished, given current research.

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Ecological speciation! Or the lack thereof?This Perspective is based on the author’s J.C. Stevenson Memorial Lecture delivered at the Canadian Conference for Fisheries Research in Halifax, Nova Scotia, January 2008.

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f09-074 ◽

2009 ◽

Vol 66 (8) ◽

pp. 1383-1398 ◽

Cited By ~ 133

Author(s):

Andrew P. Hendry

Keyword(s):

Nova Scotia ◽

Reproductive Isolation ◽

Biological Diversity ◽

Ecological Speciation ◽

Divergent Selection ◽

Adaptive Divergence ◽

Memorial Lecture ◽

Darwin’S Finches ◽

Apparent Deviation ◽

Different Populations

Ecological speciation occurs when adaptation to different environments or resources causes the evolution of reproductive isolation. This process is now thought to be very important in the evolution of biological diversity. Indeed, support for ecological speciation is so often asserted in the literature that one can get the impression of ubiquity. Eager to ride on the coattails of this exciting work, my own research has investigated ecological speciation in guppies, sticklebacks, and Darwin’s finches. Much to my initial dismay, I failed to find simple and strong signatures of ecological speciation in the first two of these systems. Setting aside the possibility of personal incompetence, my apparent deviation from ubiquity might simply reflect an existing literature bias. This bias seems obvious in retrospect given that essentially all published studies of ecological speciation purport to be confirmatory, whereas many cases of divergent selection and adaptive divergence are associated with only weak to modest levels of reproductive isolation. In short, different populations can be arrayed along a continuum from panmixia to complete reproductive isolation. Variation along this continuum might profitably be used for studying factors, outlined herein, that can promote or constrain “progress” toward ecological speciation.

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Parasites contribute to ecologically dependent postmating isolation in the adaptive radiation of three-spined stickleback

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2016.0691 ◽

2016 ◽

Vol 283 (1836) ◽

pp. 20160691 ◽

Cited By ~ 7

Author(s):

Aliya El Nagar ◽

Andrew D. C. MacColl

Keyword(s):

Reproductive Isolation ◽

Adaptive Radiation ◽

Strong Evidence ◽

Parasite Species ◽

Ecological Speciation ◽

Population Divergence ◽

Parasitic Infections ◽

Wild Populations ◽

Postmating Isolation ◽

Theory And Model

Spatial variation in parasitic infections is common, and has the potential to drive population divergence and the reproductive isolation of hosts. However, despite support from theory and model laboratory systems, little strong evidence has been forthcoming from the wild. Here, we show that parasites are likely to cause reproductive isolation in the adaptive radiation of three-spined stickleback. Adjacent wild populations on the Scottish island of North Uist differ greatly and consistently in the occurrence of different parasites that have substantial effects on fitness. Laboratory-reared fish are more resistant to experimental infection by parasite species from their own population. Furthermore, hybrid backcrosses between the host populations are more resistant to parasites from the parental population to which they are more closely related. These patterns provide strong evidence that parasites can cause ecological speciation, by contributing to selection against migrants and ecologically dependent postmating isolation.

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Gradient Evolution of Body Colouration in Surface- and Cave-DwellingPoecilia mexicanaand the Role of Phenotype-Assortative Female Mate Choice

BioMed Research International ◽

10.1155/2013/148348 ◽

2013 ◽

Vol 2013 ◽

pp. 1-15 ◽

Cited By ~ 10

Author(s):

David Bierbach ◽

Marina Penshorn ◽

Sybille Hamfler ◽

Denise B. Herbert ◽

Jessica Appel ◽

...

Keyword(s):

Natural Selection ◽

Reproductive Isolation ◽

Assortative Mating ◽

Ecological Speciation ◽

Divergent Selection ◽

Gradual Change ◽

Cave Fish ◽

Resident Male ◽

Poecilia Mexicana ◽

Body Colouration

Ecological speciation assumes reproductive isolation to be the product of ecologically based divergent selection. Beside natural selection, sexual selection via phenotype-assortative mating is thought to promote reproductive isolation. Using the neotropical fishPoecilia mexicanafrom a system that has been described to undergo incipient ecological speciation in adjacent, but ecologically divergent habitats characterized by the presence or absence of toxic H2S and darkness in cave habitats, we demonstrate a gradual change in male body colouration along the gradient of light/darkness, including a reduction of ornaments that are under both inter- and intrasexual selection in surface populations. In dichotomous choice tests using video-animated stimuli, we found surface females to prefer males from their own population over the cave phenotype. However, female cave fish, observed on site via infrared techniques, preferred to associate with surface males rather than size-matched cave males, likely reflecting the female preference for better-nourished (in this case: surface) males. Hence, divergent selection on body colouration indeed translates into phenotype-assortative mating in the surface ecotype, by selecting against potential migrant males. Female cave fish, by contrast, do not have a preference for the resident male phenotype, identifying natural selection against migrants imposed by the cave environment as the major driver of the observed reproductive isolation.

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Developmental rate: A unifying mechanism for sympatric divergence in postglacial fishes?

Current Zoology ◽

10.1093/czoolo/58.1.21 ◽

2012 ◽

Vol 58 (1) ◽

pp. 21-34 ◽

Cited By ~ 19

Author(s):

Megan V. Mcphee ◽

David L. G. Noakes ◽

Fred W. Allendorf

Keyword(s):

Gene Flow ◽

Reproductive Isolation ◽

Genetic Recombination ◽

Rapid Evolution ◽

Developmental Rate ◽

Ecological Speciation ◽

Divergent Selection ◽

Fish Populations ◽

Trophic Polymorphism ◽

Individual Traits

Abstract Morphologically divergent ecotypes arise in fish populations on postglacial time scales, and resource polymorphisms are often invoked to explain their origin. However, genetic recombination can constrain the ability of divergent selection to produce reproductive isolation in sympatry. Recombination breaks up favorable combinations of traits (“adaptive suites”) if individual traits are affected by different loci. Recombination also breaks up any association between traits under divergent selection and traits contributing to reproductive isolation. Thus, ecological speciation in the absence of preexisting barriers to gene flow is more likely when pleiotropy minimizes the number of loci involved. Here, we revisit research conducted by Carl Hubbs in the early 1900s on the effects of developmental rate on morphological traits in fishes. Hubbs’ work provides a mechanism to explain how sympatric divergence by trophic polymorphism can occur despite the challenges of recombination. We consider the implications of Hubbs’ observations for ecological speciation with gene flow in fishes, as well as rapid evolution in captive fish populations.

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Larval Performance in the Context of Ecological Diversification and Speciation inLycaeidesButterflies

International Journal of Ecology ◽

10.1155/2012/242154 ◽

2012 ◽

Vol 2012 ◽

pp. 1-13 ◽

Cited By ~ 5

Author(s):

Cynthia F. Scholl ◽

Chris C. Nice ◽

James A. Fordyce ◽

Zachariah Gompert ◽

Matthew L. Forister

Keyword(s):

Reproductive Isolation ◽

Host Plants ◽

Oviposition Preference ◽

Ecological Speciation ◽

Larval Performance ◽

Ecological Traits ◽

Ecological Diversification ◽

Behavioral Traits ◽

Plant Effects

The role of ecology in diversification has been widely investigated, though few groups have been studied in enough detail to allow comparisons of different ecological traits that potentially contribute to reproductive isolation. We investigated larval performance within a species complex ofLycaeidesbutterflies. Caterpillars from seven populations were reared on five host plants, asking if host-specific, adaptive larval traits exist. We found large differences in performance across plants and fewer differences among populations. The patterns of performance are complex and suggest both conserved traits (i.e., plant effects across populations) and more recent dynamics of local adaptation, in particular forL. melissathat has colonized an exotic host. We did not find a relationship between oviposition preference and larval performance, suggesting that preference did not evolve to match performance. Finally, we put larval performance within the context of several other traits that might contribute to ecologically based reproductive isolation in theLycaeidescomplex. This larger context, involving multiple ecological and behavioral traits, highlights the complexity of ecological diversification and emphasizes the need for detailed studies on the strength of putative barriers to gene flow in order to fully understand the process of ecological speciation.

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Mental well-being interventions in the military: The ten key principles

BMJ Military Health ◽

10.1136/bmjmilitary-2020-001740 ◽

2021 ◽

pp. bmjmilitary-2020-001740

Author(s):

Erin G Lawrence ◽

N Jones ◽

N Greenberg ◽

N T Fear ◽

S Wessely ◽

...

Keyword(s):

Armed Forces ◽

Well Being ◽

The United Kingdom ◽

Raising Awareness ◽

Mental Health Interventions ◽

External Training ◽

The Military ◽

Mental Well Being ◽

Single Versus

Organisations including the United Kingdom Armed Forces should seek to implement mental health interventions to increase the psychological well-being of their workforce. This editorial briefly presents ten key principles that military forces should consider before implementing such interventions. These include job-focused training; evaluating interventions; the use of internal versus external training providers; the role of leaders; unit cohesion, single versus multiple session psychological interventions; not overgeneralising the applicability of interventions; the need for repeated skills practice; raising awareness and the fallibility of screening.

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Speciation and changes in male gene expression in Drosophila

Genome ◽

10.1139/gen-2020-0025 ◽

2020 ◽

pp. 1-11

Author(s):

Bahar Patlar ◽

Alberto Civetta

Keyword(s):

Gene Expression ◽

Reproductive Isolation ◽

Potential Role ◽

Regulation Of Gene Expression ◽

Drosophila Model ◽

Depth Analysis ◽

The Impact ◽

Plastic Responses ◽

Male Gene

It has long been acknowledged that changes in the regulation of gene expression may account for major organismal differences. However, we still do not fully understand how changes in gene expression evolve and how do such changes influence organisms’ differences. We are even less aware of the impact such changes might have in restricting gene flow between species. Here, we focus on studies of gene expression and speciation in the Drosophila model. We review studies that have identified gene interactions in post-mating reproductive isolation and speciation, particularly those that modulate male gene expression. We also address studies that have experimentally manipulated changes in gene expression to test their effect in post-mating reproductive isolation. We highlight the need for a more in-depth analysis of the role of selection causing disrupted gene expression of such candidate genes in sterile/inviable hybrids. Moreover, we discuss the relevance to incorporate more routinely assays that simultaneously evaluate the potential effects of environmental factors and genetic background in modulating plastic responses in male genes and their potential role in speciation.

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Introgression between non-sister species of honeyeaters (Aves: Meliphagidae) several million years after speciation

Biological Journal of the Linnean Society ◽

10.1093/biolinnean/blz129 ◽

2019 ◽

Vol 128 (3) ◽

pp. 583-591

Author(s):

Leo Joseph ◽

Alex Drew ◽

Ian J Mason ◽

Jeffrey L Peters

Keyword(s):

Gene Flow ◽

Reproductive Isolation ◽

Sex Chromosomes ◽

Common Ancestor ◽

Sister Species ◽

Species Boundaries ◽

North Eastern ◽

The City

Abstract We reassessed whether two parapatric non-sister Australian honeyeater species (Aves: Meliphagidae), varied and mangrove honeyeaters (Gavicalis versicolor and G. fasciogularis, respectively), that diverged from a common ancestor c. 2.5 Mya intergrade in the Townsville area of north-eastern Queensland. Consistent with a previous specimen-based study, by using genomics methods we show one-way gene flow for autosomal but not Z-linked markers from varied into mangrove honeyeaters. Introgression barely extends south of the area of parapatry in and around the city of Townsville. While demonstrating the long-term porosity of species boundaries over several million years, our data also suggest a clear role of sex chromosomes in maintaining reproductive isolation.

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